docs: def list(gandi, datacenter, id, subnet, gateway):
      """List vlans."""
      output_keys = ['name', 'state', 'dc']
      if id:
          output_keys.append('id')
      if subnet:
          output_keys.append('subnet')
      if gateway:
          output_keys.append('gateway')
  
      datacenters = gandi.datacenter.list()
  
      vlans = gandi.vlan.list(datacenter)
      for num, vlan in enumerate(vlans):
          if num:
              gandi.separator_line()
          output_vlan(gandi, vlan, datacenters, output_keys)
  
      return vlans